This proposal describes the development of an innovative training and research tool, a novel agent-based model (ABM), to address a critical global health challenge, the devastating toll of early childhood diarrhea (ECD). An ABM will be developed to simulate the complex system of ECD, water supply and quality, enteric infection, and other environmental factors. The ABM will be created using quantitative and qualitative data relevant to the understanding of ECD previously collected from two rural communities in South Africa. The comprehensive ABM will subsequently be validated by comparison with outcome data collected prospectively in the same communities. The model will be developed by a trans-disciplinary team from the University of Virginia and the University of Venda (South Africa), incorporating medicine, public health, nursing, engineering, planning, microbiology, and environmental science. Post-doctoral trainees will be mentored to develop knowledge and skills necessary for trans-disciplinary work. They will also be provided with the opportunity to engage in the practical development and testing of the agent-based model. The specific aims are: 1. To design an agent-based model, the Water and Health in Limpopo Agent-Based Model (WHIL-ABM), to simulate the relationships between early childhood diarrhea (ECD), water supply and quality, enteric infection, and other environmental factors in two rural communities in Limpopo Province, South Africa. 2. To validate the WHIL-ABM through comparison with prospective data on child growth, water quality, and other environmental conditions collected in on-going field projects. 3. To use the development of the WHIL-ABM to create mentored training opportunities for post-doctoral students in analysis of complex systems, agent-based modeling, data collection, environmental assessment, community engagement, and global health research ethics. 4. To foster meaningful trans-disciplinary faculty collaboration at the University of Virginia (UVa) and the University of Venda (UNIVEN). 5. To conduct a workshop on agent-based modeling at the University of Venda to reinforce the on-going collaboration and build the capacity of faculty and post-graduate students in complex system analysis. PUBLIC HEALTH RELEVANCE: Researchers have struggled for decades in resource-limited communities to develop and implement effective and sustainable strategies to decrease ECD through the improvement of water and sanitation. The development of an ABM that describes a community with endemic ECD will allow researchers to test hypotheses in silico, facilitating the identification of the most promising hypothetical interventions and accelerating the development of sustainable strategies to reduce the devastating costs of ECD.